Bioleaching potential of local bacteria from gold mine tailings in the Ratatotok Area, Indonesia

Our previous study found that Bacillus cereus from the rhizosphere of Syzygium aromaticum (RTKS) exhibited the highest resistance and the best gold bioleaching potential at pH 8. However, this bacteria’s potential requires further investigation. The current study aimed to (1) determine the temperature that supports the effectiveness of B. cereus RTKS in the bioleaching of gold, and (2) test the effectiveness of bioleaching by B. cereus RTKS with variations in Au contents in tailings. The experiment began by growing bacteria in a medium, which was then inoculated into tailing effluent. The experiment was carried out in an Erlenmeyer flask shaken at 120 rpm for 3 weeks. In the first-stage experiment, temperatures of 25°C and 50°C were tested. The optimum temperature obtained in the first stage was then used for the second-stage experiment with variations in Au contents in tailings. After bioleaching, the filtration process was conducted and produced three components, namely pellets containing bacterial cells, supernatants, and residues. Bacteria mentioned above were more effective in bioleaching of gold at a temperature of 50° C than at 25°C, indicated by higher Au extraction in pellets and residues, and Au accumulation which tended to be higher in pellets. In treatments with varying Au concentrations in the tailings, increasing Au content did not lead to higher Au accumulation by B. cereus RTKS. The Au content in the residue was significantly highest in the tailings bioleaching treatment with the highest Au content.